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CAPEC-99: XML Parser Attack

Attack Pattern ID: 99
Abstraction: Standard
Status: Draft
Presentation Filter:
+ Description
Applications often need to transform data in and out of the XML format by using an XML parser. It may be possible for an attacker to inject data that may have an adverse effect on the XML parser when it is being processed. These adverse effects may include the parser crashing, consuming too much of a resource, executing too slowly, executing code supplied by an attacker, allowing usage of unintended system functionality, etc. An attacker's goal is to leverage parser failure to his or her advantage. In some cases it may be possible to jump from the data plane to the control plane via bad data being passed to an XML parser. [R.99.1]
+ Likelihood Of Attack

Medium

+ Typical Severity

Medium

+ Relationships

The table(s) below shows the other attack patterns and high level categories that are related to this attack pattern. These relationships are defined as ChildOf, ParentOf, MemberOf and give insight to similar items that may exist at higher and lower levels of abstraction. In addition, relationships such as CanFollow, PeerOf, and CanAlsoBe are defined to show similar attack patterns that the user may want to explore.

+ Relevant to the view "Mechanisms of Attack" (CAPEC-1000)
NatureTypeIDName
ChildOfStandard Attack PatternStandard Attack Pattern - A standard level attack pattern in CAPEC is focused on a specific methodology or technique used in an attack. It is often seen as a singular piece of a fully executed attack. A standard attack pattern is meant to provide sufficient details to understand the specific technique and how it attempts to accomplish a desired goal. A standard level attack pattern is a specific type of a more abstract meta level attack pattern.82Violating Implicit Assumptions Regarding XML Content (aka XML Denial of Service (XDoS))
+ Execution Flow
Explore
  1. An attacker determines the input data stream that is being processed by an XML parser on the server side.

Experiment
  1. An attacker crafts input data that may have an adverse effect on the operation of the XML parser when the data is parsed on the server.

+ Prerequisites
An application uses an XML parser to perform transformation on user-controllable data.
An application does not perform sufficient validation to ensure that user-controllable data is safe for an XML parser.
+ Skills Required
[Level: Low]
Denial of service (making the parser crash)
[Level: High]
Arbitrary code execution
+ Indicators
Bad data is continuously passed to the XML parser, possibly making it crash.
+ Consequences

The table below specifies different individual consequences associated with the attack pattern. The Scope identifies the security property that is violated, while the Impact describes the negative technical impact that arises if an adversary succeeds in their attack. The Likelihood provides information about how likely the specific consequence is expected to be seen relative to the other consequences in the list. For example, there may be high likelihood that a pattern will be used to achieve a certain impact, but a low likelihood that it will be exploited to achieve a different impact.

ScopeImpactLikelihood
Availability
Resource Consumption
Confidentiality
Read Data
Confidentiality
Integrity
Availability
Execute Unauthorized Commands
Confidentiality
Access Control
Authorization
Gain Privileges
+ Mitigations
Carefully validate and sanitize all user-controllable data prior to passing it to the XML parser routine. Ensure that the resultant data is safe to pass to the XML parser.
Perform validation on canonical data.
Pick a robust implementation of an XML parser.
Validate XML against a valid schema or DTD prior to parsing.
+ Example Instances
"PHPXMLRPC aka XML-RPC For PHP is a PHP implementation of the XML-RPC web RPC protocol, and was originally developed by Edd Dumbill of Useful Information Company. As of the 1.0 stable release, the project has been opened to wider involvement and moved to SourceForge. PHPXMLRPC is used in a large number of popular web applications such as PostNuke, Drupal, b2evolution, and TikiWiki. Unfortunately PHPXMLRPC is vulnerable to a remote php code execution vulnerability that may be exploited by an attacker to compromise a vulnerable system.
Remote Command Execution:
PHPXMLRPC is vulnerable to a very high risk remote php code execution vulnerability that may allow for an attacker to compromise a vulnerable webserver. The vulnerability is the result of unsanitized data being passed directly into an eval() call in the parseRequest() function of the XMLRPC server.
By creating an XML file that uses single quotes to escape into the eval() call an attacker can easily execute php code on the target server. This has a lot to do with the fact that magic_quotes_gpc() does not apply to $HTTP_RAW_POST_DATA so using single quotes is not a problem" [R.99.2]
See also: CVE-2005-2498
+ References
[REF-89] Shlomo, Yona. "XML Parser Attacks: A summary of ways to attack an XML Parser". What is an XML Parser Attack?. 2007. <http://yeda.cs.technion.ac.il/~yona/talks/xml_parser_attacks/slides/slide2.html>.
[REF-558] GulfTech Security Research. "PHPXMLRPC Remote Code Execution". BugTraq Archive. 2005-06-29. <http://www.securityfocus.com/archive/1/403987>.
+ Content History
Submissions
Submission DateSubmitterOrganization
2014-06-23CAPEC Content TeamThe MITRE Corporation

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Page Last Updated or Reviewed: July 31, 2018